I am trying to identify at which point during the year 80% of bird breeding observations are. Typically I would answer a question like this by finding the median or quartiles, but how do I deal with situations where 80% of the observations are from day 285 through day 366 (leap year) and extends to day 30?
The data is circular and day 365 is as close to day 366 as day 1.
I am reading the manual for CircStats and circular but I could really use some help on this.
My questions are: what is the shortest number of days where 50% of the observations are and what is the start day and end day of that period?
Here is some dummy data:
library(CircStats)
#dummy data
obsDay<-c(rep(1:30,10),rep(45:65,2),65:180,
rep(181:265,2),rep(266:330,4),rep(331:366,6))
#density plot
plot(density(obsDay))
#convert data to Radians
obsRadians <-(obsDay/366*360)*3.1459 / 180
#make a circular plot
circ.plot(obsRadians, stack=TRUE, bins=100,shrink=1.8)